1. Field of the Invention
The present invention relates to a light-emitting diode (LED) lighting apparatus and a method for fabricating a wavelength conversion member which is spaced apart from an LED in the LED lighting apparatus and converts a wavelength of light emitted from the LED.
2. Description of the Related Art
As light sources for illumination, fluorescent lamps and incandescent bulbs have been widely used. Incandescent bulbs have low efficiency and economic feasibility due to their high power consumption. For this reason, the demand for incandescent bulbs tends to significantly decrease. It is expected that such a decreasing trend will continue in the future. On the contrary, since fluorescent lamps have about ⅓ of power consumption of incandescent bulbs, they are high-efficient and cost-efficient. However, since fluorescent lamps are blackened by application of high voltage, the lifespan of fluorescent lamps is short. In addition, fluorescent lamps are environmentally unfriendly because they use a vacuum glass tube into which mercury being a heavy metal is injected together with argon gas.
Recently, the demand for LED lighting apparatuses has been rapidly increasing. LED lighting apparatuses have a long lifespan and are driven with low power. In addition, LED lighting apparatuses are environmentally friendly because they use no environmentally harmful substances such as mercury. A typical LED lighting apparatus includes an LED module, and the LED module includes package-level or chip-level LEDs, and a printed circuit board (PCB) on which the LEDs are mounted. Each of the LEDs includes an LED chip configured to emit light in a specific wavelength range, and a wavelength conversion material (for example, a phosphor) configured to generate desired color light, especially white light, by converting a wavelength of light emitted from the LED chip. Generally, the wavelength conversion material is included in an encapsulation material covering the LED chip, or is directly formed on the LED by conformal coating.
In the LED lighting apparatus, much heat is generated when the LEDS are supplied with power and operated. This heat has a bad influence on the wavelength conversion material included in the encapsulation material covering the LED chip or directly formed on the LED chip. That is, the encapsulation material including the wavelength conversion material may be separated from the surface of the LED chip by heat, and the original characteristic of the wavelength conversion material may be changed by heat. Therefore, feature values, such as color coordinates or color temperature of light generated by the LED lighting apparatus, may deviate from an originally intended or designed range.
In this regard, there has been proposed an LED lighting apparatus configured such that an optical member or an optical cover spaced apart from LEDs includes phosphors. Since the optical member is spaced apart from the LEDs, the phosphors included in the optical member may not be badly affected by heat generated from the LEDs. As a method of adding the phosphors to the inside of the optical member, there are a method of molding an optical member with a resin material mixed with phosphors, and a method of coating a phosphor on one surface of an optical member in a printing technique. Since the former method is limited to the molding technique using the resin material, it is difficult to apply to an optical member such as a glass. In addition, air bubbles may be formed within the optical member together with the phosphors. According to the latter method, the phosphor layer is formed on one surface of the optical member. The phosphor layer is formed with an uniform surface in the early stage, but the surface of the phosphor layer may be rough as times goes by. In worse cases, the phosphor layer may be separated from the surface of the optical member.